Leak indicator for vacuum systems and a method of searching for leaks in vacuum systems

ABSTRACT

A leak indicator for detecting leaks in a vacuum system including a chamber and a system vacuum pump. The indicator is provided with a mass spectrometer for identifying the presence of a test gas in the system chamber and a high vacuum pump for producing the pressure required for operation of the mass spectrometer during a system leak test. A sealed conduit network is provided to connect the system chamber to the inlet of the mass spectrometer, and to the inlet side and exhaust side of the high vacuum pump. A first switching valve is provided within the sealed conduit in series between the system chamber and the inlets of the mass spectrometer and the high vacuum pump. Lastly, a constriction member is connected within the network conduit in series between the system chamber and the first switching valve to selectively provide a direct connection between the system chamber and the inlet side of the high vacuum pump, or between the system chamber and the exhaust side of the high vacuum pump.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns a leak indicator for vacuum systems comprising achamber which is evacuated while the system is in operation plus avacuum pump used to evacuate the chamber whereby the leak indicator hasa test-gas detector in the form of a mass spectrometer plus a highvacuum pump to produce the vacuum necessary for operation of the massspectrometer.

2. Discussion of the Related Art

Before operation, after maintenance or repair work and also after otherinterruptions of operation, vacuum systems must be tested for thepresence of leaks so as to ensure optimum operating conditions of thevacuum system which are not adversely influenced by flows of leakinggas.

From DE-OS 33 16 765 a method and device is known for the detection ofleaks on turbine casings. A low pressure is maintained in the turbinecasings with the aid of vacuum pumps. For the purpose of leak detectionall parts of the turbine casing where a leak is suspected are sprayedfrom the outside with a test gas, preferably helium. The exhaust gas ofthe vacuum pumps is monitored with the aid of a sniffer leak indicatorso that the presence of any leaks can be determined. Leak detection ofthis kind is relatively insensitive.

Moreover, the leak detection arrangement for this task is fairly largeand heavy, because such an arrangement must include a complete highvacuum system with a heavy backing pump.

OBJECTS AND SUMMARY OF THE INVENTION

It is the object of the present invention to increase detectionsensitivity of the leak detection process on vacuum systems while at thesame time reducing the technical complexity of the arrangement.

This object is accomplished according to the present invention by leakindicator as outlined above by making the chamber of the vacuum systemconnectable to the inlet and/or exhaust side of the high vacuum pump inthe leak indicator via a constriction. The introduction of a suitablyrated constriction ensures that the pressure in the mass spectrometerremains sufficiently low. Due to the direct connection between thechamber of the vacuum system and the leak indicator, the flow paths forthe test gas between a possibly present leak and the mass spectrometerdetector are considerably shorter compared to the state-of-the-artthereby offering improved sensitivity and a reduction of complexity.

A particularly advantageous further development is, that theconstriction is made to act as a control valve. With the aid of thiscontrol valve the gas flowing into the mass spectrometer detector can bethrottled in such a way, that the pressure in the mass spectrometer canbe maintained at a constant level, irrespectively of the processpressure in the system and this preferably at an optimum high totalpressure of approximately 10⁻⁴ mbar. In such a mode of operation theleak indicator will operate as a concentration measuring instrument forthe test gas, so that the interfering gas concentration in the processis indicated to the persons responsible for running the process.Concentration changes are measured correctly and independently of anytotal pressure variations during the process, even if the leak rateitself remains constant (the leak rate is only the cause for thequantity of the gas concentration which interferes with the process).

A further advantageous measure is, to employ a pump system in the leakindicator which consists of a high vacuum pump and a further pumpingstage, so that on the pressure side of the pump system a pressure can beproduced which is of the same order of magnitude compared to theoperating pressure within the chamber of the vacuum system, 40 mbar, forexample. With such a pump system it is possible to connect the exhaustof the pump system to the chamber of the vacuum system, so that it willno longer be required to equip the leak indicator itself with a backingpump. Thus the leak indicator is light-weight and especially handy whichis of great importance especially during leak detection on large fixedinstallations.

BRIEF DESCRIPTION OF THE DRAWING

Further objectives, advantages and details of the invention will becomeapparent from the following description taken in conjunction with theexamples in drawing FIGS. 1 to 3, wherein:

FIG. 1 is a schematic representation of a first example of the presentvacuum system leak indicator;

FIG. 2 is another schematic representation of a second example of a leakindicator in accordance with the present invention; and

FIG. 3 is yet another schematic representation of a third example of thepresent leak indicator according to this invention.

DETAILED DESCRIPTION OF THE INVENTION

Shown in the drawing figures is the vacuum system 1 in which leaks areto be detected, its vacuum chamber 2 and the pump 3 which belongs to thevacuum system 1.

The leak indicator which is generally marked 4 is directly connectablevia flange connection 5 to chamber 2. It comprises mass spectrometerdetector 6 and high vacuum pump 7 which is preferably a turbomolecularpump. Via line 8 with constriction 9 the chamber 2 may be connecteddirectly to the inlet side of the high vacuum pump, i.e. directly todetector 6. A line 11 leading to the exhaust side of the high vacuumpump branches off from line 8--in the flow direction of a possiblyflowing test gas from chamber 2 to mass spectrometer detector 6--afterconstriction 9 so that the chamber 2 of vacuum system 1 may also beconnected via constriction 9 to this point on leak indicator 4.Switching valves 12 and 13 control the desired gas flow.

In the example according to drawing FIG. 1 the high vacuum pump 7 isfollowed by a common backing pump 14. The leak detection process isperformed in such a way, that the chamber 2 of vacuum system 1 issprayed from the outside with test gas. In order to determine a possiblypresent coarse leak, the connection between chamber 2 and the exhaustside of the high vacuum pump 7 is initially provided via theconstriction 9 (valve 12 open, valve 13 closed). Any test gas whichmight flow through this path enters into the mass spectrometer 6 againstthe pumping direction of the high vacuum pump 7, whereby the indicatingdevices for the mass spectrometer 6 are not shown. The sensitivity ofthe leak detection process can be increased by opening valve 13 so thatthe test gas is admitted directly to the detector.

The size of constriction 9 must be such, that the pressure required foroperation of the mass spectrometer 6 is not exceeded. It is particularlyadvantageous to let the constriction act as a control valve which iscontrolled by the pressure in the mass spectrometer 6 in such a way,that this pressure is maintained at a constant level. In this mode ofoperation the leak indicator will operate as a concentration measuringinstrument, whereas in the case of a fixed constriction or when thecontrol valve 9 is set to a fixed value, it will function as a leak ratemeasuring instrument. The means used to control the control valve 9 areonly shown schematically in drawing FIG. 1. They comprise the controlsystem 15 shown as a block which is supplied with the necessaryinformation concerning the pressure in the mass spectrometer detector 6via line 16. Number 17 is used to mark a pressure gauge which indicatesthe pressure in detector 6. A pressure rise in chamber 2 will result ina pressure rise also in the detector 6 when the constriction 9 is set toa fixed value. In the case of a rising pressure in chamber 2 thepresented control system will provide a stronger throttling effect ofcontrol valve 9, so that the pressure in detector 6 is maintained at aconstant level.

In the example according to drawing FIG. 2 the high vacuum pump 7 isfollowed by a diaphragm pump 21 which is of a dual-stage design. It ispreferably designed in such a way, that it is capable of producing anexhaust pressure of about 40 to 100 mbar based on an inlet pressure ofabout 0.1 mbar. In this case it is possible to connect the exhaust line22 to the chamber 2 so that a blocking pump in leak indicator 4 whichcompresses the gas to atmospheric pressure is not required. In order toavoid two connection lines between chamber 2 and the leak indicator 4,line 22 leads into line 8 within the leak indicator 4 at a point betweenthe inlet valve 2 and the constriction 9.

In the example according to drawing FIG. 3 the pump which follows thehigh vacuum pump 7 is of the screw or molecular pump stage type 23.Combined turbomolecular/molecular vacuum pumps the rotors of which arearranged on a common shaft, are known in the mean time and also exhibitthe forevacuum capabilities described in the example of drawing FIG. 2,so that it also will be possible to return the exhaust line 22 tochamber 2 and so to dispense with a separate blocking pump in leakindicator 4.

With the designs detailed in drawing FIGS. 2 and 3 it is possible to runthe leak detection process on the system 1 at three levels ofsensitivity. Pre-requisite for this is, that also line 11 be equippedwith a valve 24. When wanting to detect particularly large leaks, valves13 and 24 are closed so that any test gas which possibly enters thechamber 2 can only arrive at the detector 6 via lines 22 and against thepumping direction of pump stages 7, 21 or 7, 23. For the purpose ofincreasing the sensitivity then first valve 24 and then valve 13 may beopened.

While this invention has been described in detail with reference tocertain examples, it should be appreciated that the present invention isnot limited to those precise examples. Rather, in view of the presentdisclosure which describes the best mode for practicing the invention,many modifications and variations would present themselves to those ofskill in the art without departing from the scope and spirit of thisinvention, as defined in the following claims.

What is claimed is:
 1. A leak indicator apparatus for detecting leaks ina vacuum system comprising:a system chamber and a system vacuum pumpattached to said system chamber; a mass spectrometer-having an inlet,said mass spectrometer for identifying the presence of a test gas in thesystem chamber; a high vacuum pump having a inlet side and an exhaustside, said high vacuum pump with said system pump adapted to produce thelow vacuum pressure required for operation of said mass spectrometerduring a system leak test; a sealed conduit network connecting thesystem chamber to the inlet of said mass spectrometer, and the systemchamber to the inlet side and exhaust side of said high vacuum pump; afirst switching valve connected within said sealed conduit network inseries between the system chamber and the inlets of said massspectrometer and said high vacuum pump; and a constriction memberconnected within said sealed conduit network in series between thesystem chamber and said first switching valve whereby control of saidfirst switching valve alternatively allows a direct connection betweenthe system chamber and the inlet side of said high vacuum pump, and thesystem chamber and the exhaust side of said high vacuum pump.
 2. Theleak indicator apparatus according to claim 1 further including a secondswitching valve connected within said sealed conduit network between thesystem chamber and said constriction member, said second switching valveproviding a closable fluid connection between the chamber and theconduit network.
 3. The leak indicator apparatus according to claim 1wherein said constriction member is a control valve adapted to vary thepressure difference thereacross.
 4. The leak indicator apparatusaccording to claim 1 further including a dual-stage diaphragm pumpconnected at one side thereof to the exhaust side of said high vacuumpump and at another side thereof into said sealed conduit networkbetween the system chamber and said constriction member, said dual-stagediaphragm pump capable of producing an output pressure of the same orderof magnitude as the pressure within the system chamber.
 5. The leakindicator apparatus according to claim 4 further including a thirdswitching valve connected at one side thereof to the exhaust side ofsaid high vacuum pump and at another side thereof into said sealedconduit network between said first switching valve and said constrictionmember.
 6. The leak indicator apparatus according to claim 1 furtherincluding a screw pump connected at one side thereof to the exhaust sideof said high vacuum pump and at another side thereof into said sealedconduit network between the system chamber and said constriction member,said screw pump capable of producing an output pressure of the sameorder of magnitude as the pressure within the system chamber.
 7. Theleak indicator apparatus according to claim 6 further including a thirdswitching valve connected at one side thereof to the exhaust side ofsaid high vacuum pump and at another side thereof into said sealedconduit network between said first switching valve and said constrictionmember.
 8. The leak indicator apparatus according to claim 1 furtherincluding a molecular pump connected at one side thereof to the exhaustside of said high vacuum pump and at another side thereof into saidsealed conduit network between the system chamber and said constrictionmember, said molecular pump capable of producing an output pressure ofthe same order of magnitude as the pressure within the system chamber.9. The leak indicator apparatus according to claim 8 further including athird switching valve connected at one side thereof to the exhaust sideof said high vacuum pump and at another side thereof into said sealedconduit network between said first switching valve and said constrictionmember.
 10. A method for detecting a leak in a vacuum system including asystem chamber and a system vacuum pump, said method comprising thesteps of:connecting the system chamber to a leak indicator including ahigh vacuum pump with inlet side and exhaust side, which high vacuumpump is connected to a mass spectrometer and a control valve as aconstriction member in series with a switching valve for fluidlyconnecting the system chamber directly to either side of the high vacuumpump, where the high vacuum pump with said system pump is adapted toproduce the low pressure required for operation of said massspectrometer during a system leak test; spraying a test gas tracerproximate areas of the vacuum system suspected of having leaks; andthrottling gas flow into the mass spectrometer by adjusting the controlvalve to maintain a substantially constant pressure within the massspectrometer.
 11. The method according to claim 10 wherein said sprayingstep includes use of helium as the test gas.